Despite many new medications and technologies to improve diabetes self-management and glycemic control (blood glucose [BG] levels), disability and premature mortality from chronic diabetes complications remain common, highlighting the gap between treatment advances and robust patient uptake. Non-adherence to prescribed diabetes treatment contributes significantly to this gap, especially in the vulnerable population o mid to older teens with type 1 diabetes (T1D) who are emerging from their parents' care and becoming more independent in their own self-care. During this developmental period, glycemic control often deteriorates as adherence to BG monitoring declines. Longitudinal studies reveal that non-adherence in late adolescence is a risk factor for poor glycemic control, multiple physical and psychiatric comorbidities, and premature mortality. The primary aim of the proposed project is to improve glycemic control, measured as hemoglobin A1c (A1c) (an index of average BG levels over the previous 2-3 months), by motivating self-care behaviors in mid to older teens with T1D, ages 14-17 years old. Given the complex and often intractable nature of non- adherence in adolescence, this application proposes to design, implement, and evaluate multi-faceted interventions aimed at increasing adherence, particularly to BG monitoring, and improving glycemic control. These interventions include: (1) a behavioral Teen work (TW) intervention targeting BG monitoring and diabetes self-management through increased self-efficacy, (2) automated 2-way text message reminders to check BG levels (TX), or (3) both (TW/TX). The proposed project extends our Family Teamwork intervention, previously validated in school-age children and young teens with T1D, by tailoring it to mid to older teens with T1D, and also builds on our pilot work of 2-way text message reminders to increase BG monitoring frequency. The Teen work intervention is focused on self-care behaviors and is integrated into the teen's regular quarterly diabetes clinic visits. Grounded in social cognitive theory, this multiple-PI R01 randomized controlled clinical trial will be implemented at 2 large diabetes clinical sites. We propose a 2x2 factorial design in which 300 mid to older teens with T1D duration of e1 year and A1c levels of 7-13% will be randomized to 1 of 4 groups: TW, TX, TW/TX, or Standard Care (SC). In this 2-year study, the primary outcome will be change in A1c from baseline to 12 months across the 4 groups, as well as from 12 to 24 months. To ensure recruitment and retention of this at-risk population, the SC group will cross-over to TW/TX at 12 months. The TW, TX, and TW/TX groups will continue to receive their respective interventions in months 12-24 to assess durability. We will assess BG monitoring frequency and A1C, as well as other measures for mode rational and meditational analyses. Data will be collected on costs of the interventions and any adverse outcomes to assess if the interventions enhance adherence to BG monitoring and improve A1c cost-effectively in mid to older teens with T1D as they prepare to transition to young adulthood and diabetes self-care.